Paraffin solubility curves of diesel fuels from thermodynamic model adjusted through experimental DSC thermograms

DSC and wax solubility curves were measured for two diesel fuel samples. Compositional profiles were also measured for the solubility curve points. The paraffin distributions of the samples were determined and the non-paraffinic components were lumped into pseudocomponents. The liquid phase was modeled using the Peng-Robinson equation of state with the classical van der Waals mixing rule. For the solid phase, the modified UNIQUAC model was employed. The models were fitted to the DSC data by tuning only four multipliers acting on the molecular weights, boiling and critical temperatures of the pseudocomponents as well as on the paraffins' pair interaction energies from the UNIQUAC model. Then the model is used to predict wax appearance temperature, amount and composition of solid deposit as a function of temperature during cooling. Excellent results were obtained for the two samples analyzed. This way, the methodology developed is able to predict adequately the formation of solid paraffin from diesel fuels.